1. Field of the Invention
The present invention relates to a washing machine and a method of controlling the same, and more particularly, to a washing machine which washes laundry by wobbling a washing board thereof and a method of controlling the same.
2. Description of the Related Art
Generally, a washing machine is an apparatus which washes laundry by rotating a cylindrical rotating tub containing the laundry and washing water. Such washing machines may be divided into drum-type washing machines and vertical-axis washing machines. A drum-type washing machine allows a rotating tub to be horizontally disposed, and washes laundry using impact that is obtained as the laundry is lowered by gravitation, after being raised up along an inner surface of the rotating tub, while the rotating tub is rotated around a horizontal axis in forward and reverse directions. In contrast, a vertical-axis washing machine allows a spin-drying tub equipped with a pulsator therein to be vertically disposed, and washes laundry using water currents generated by the pulsator, while the spin-drying tub is rotated around a vertical axis in forward and reverse directions. In conventional drum-type washing machines and vertical-axis washing machines, the amount of laundry is ascertained by detecting a number of rotations of a motor that are caused by inertia, once a driving of a rotating spin-drying tub or a pulsator is stopped.
Another type of vertical-axis washing machine has a wobbling device and washes laundry by exerting a mechanical impact to the laundry, in upward and downward directions, through the use of the wobbling device which reciprocates in upward and downward directions. Such a wobbling washing machine uses a mechanical impact energy generated by the wobbling device, instead of currents of wash water, and requires a smaller amount of wash water and detergent as compared to the general vertical-axis washing machine described above.
FIG. 1 shows an inner structure of a conventional vertical-axis washing machine having a wobbling device which is situated in, for example, a level position. A “wobbling position” indicates a position in which the wobbling device allows a washing board of the washing machine to be slantingly disposed so as to have the washing board be wobbled in upward and downward directions. A “level position” indicates a position in which the wobbling device allows the washing board to be horizontally disposed so as not to have a wobbling of the washing board.
As shown in FIG. 1, the washing machine comprises a housing 1, a water tub 2 mounted in the housing 1, a spin-drying tub 3 mounted inside of the water tub 2 and provided with a plurality of drain holes 3c, a drive motor 5 and a power transmission unit 6 mounted under the water tub 2, and a wobbling device 20 mounted in the lower portion of the spin-drying tub 3.
A drain hose 8 is provided under the water tub 2 and extends to the outside so as to drain wash water contained in the water tub 2 to the outside of the washing machine after a washing operation. A pump motor 11 and a restoring pipe 12 which circulate the wash water supplied to the water tub 2 to an upper portion of the water tub 2 are provided as shown, so as to reduce the amount of water used. Additionally, a water supply valve 13 is disposed in a water supply conduit connected to an outside hydrant (not shown).
A spin-drying shaft support 9 is mounted on an outer surface of a bottom 3a of the spin-drying tub 3. A spin-drying shaft 6a of the power transmission unit 6 is fitted into a center of the spin-drying shaft support 9 and rotates the spin-drying tub 3. A washing shaft 6b is positioned in the spin-drying shaft 6a. An upper end of the washing shaft 6b extends over an upper end of the spin-drying shaft 6a by a predetermined length to be coupled to the wobbling device 20.
FIG. 2 shows the washing machine shown in FIG. 1 with the wobbling device 20 switched to a wobbling position. The wobbling device 20 is mounted on an inner surface of the bottom 3a of the spin-drying tub 3. Where the wobbling device 20 is switched to the wobbling position as shown in FIG. 2, the washing machine washes laundry by wobbling the laundry in upward and downward directions using the wobbling device 20. Thereafter, the washing machine spin-dries the laundry by rotating the wobbling device 20, together with the spin-drying tub 3, with the wobbling device 20 switched to a level position, as shown in FIG. 1.
Where the wobbling device 20 is situated in the wobbling position, the wobbling device 20 is rotated by a rotating force of the drive motor 5. However, the rotating movement of the wobbling device 20 is converted into a rectilinear movement, and this rectilinear movement is transmitted to the laundry. Accordingly, detecting an amount of the laundry through detecting a number of rotations of the drive motor 5 is not effective in such a case. Additionally, where the wobbling device 20 is situated in the level position, the wobbling device 20 and the spin-drying tub 3 are rotated together by a rotation of the drive motor 5. Accordingly, in this case, the amount of laundry cannot be effectively detected by detecting a number of rotations of the drive motor 5.